Arpana Arjun works in the Panagiotakis Lab at Eli and Edy the Broad Center of Regeneration Medicine and Stem Cell Research at UCSF Parnassus Campus in San Francisco, Calif., on Tuesday, September 12, 2017.

Photo: Scott Strazzante / The Chronicle 2017

California’s pioneering decision to spend $3 billion on stem cell research isn’t producing cures after 14 years of work. Instead, it’s generating a widening scientific field that shows potential but not results.

It’s a frustrating shortcoming, especially as supporters of the state-sponsored research weigh another bond measure to continue the work. Promised breakthroughs used to sell Proposition 71 in 2004 aren’t panning out, a Chronicle investigation found.

To be sure, there’s progress worth noting. Hundreds of grants are paying for basic research, preclinical work, new facilities and education. What’s missing is the crucial next step: clinical trials that could focus on diseases and conditions such as leukemia, kidney failure and cancer. Despite a few exceptions, real-world tests on humans remain distant.

There are plausible explanations for the delay. The medical endeavor that creates healthy cells to replace damaged ones has encountered legal, organizational and scientific wait times. Miraculous cures can’t be predicted or put on a schedule.

There are also practical problems that are concerning. The grant-making center of the work, the California Institute for Regenerative Medicine, was designed to be off-limits to outside interference, but that structure makes it hard to oversee or audit. The tiny world of highly refined research means that a handful of institutes and universities gobble up the money. The credentialed panel of experts who direct the institute frequently must recuse themselves from decisions because of ties to researchers. Also, for-profit operations not connected with the state effort have sprung up offering risky treatments to desperate patients.

The results to date don’t argue for expanded public spending. The science of stem cell work will need to evolve before more money is provided.

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